Particle system rotation as a whole
One part of the problem - i.e. OpenGL-rendering an emitter and its particle system being spatially transformed at a definite keyframe of a physics animation - was solved thanks to Rich Sedman comment about locking the 3D View to the camera (Numpad 0).
Yet, I also had two additional constraints:


make the physics animation as short as possible in an orthographic view and rely on its end (physics) state to produce a panoramic view of the particle system;
hide the emitter and leave the particle system alone while panoramically showing around the last frame of the physics animation;


To reach these goals, the particle animation render (Particle System ‣ Render) was chosen of type Object (or Group of objects) with a (small) UV sphere in place of each particle. In the Display panel of the emitter, I had to switch the Maximum Draw Type from Wire to Solid though Wire was enough for my purpose of showing the (haloed) particle system alone but with Object as render type it ran into the pitfall of drawing the edges of each single sphere. So, I had to rely on Transparency which had to be checked off in the same Display panel to enable the alpha channel of emitter Viewport Color set to 0 (Cycles Render).
Having run and baked the animation and selected its end frame, pink vertex (I would like to generate a particle star field that I could keep as static background) provided a super script which allowed to supersede the particles with a real mesh of point-vertices. Then, using the DupliVerts technique (Object panel ‣ Duplication ‣ Vertices), a copy of the (small) sphere chosen for the physics animation render was used to replace each point-vertex.
From this point forward, it was just a matter of making up the animation through the Dope Sheet (Action Editor) applying Restrict View / Restrict Render keyframes to show the original particle system for the actual duration of the physics animation and keep the duplicated one hidden at the same time. On the contrary, during the part of the animation which was not physically baked, the duplicated system was visible while the camera moved around and the original particle system was hidden.